1. Field of the Invention
This invention relates to an alarm system which generates an alarm signal when engine oil pressure drops excessively or is harmfully low.
2. Description of the Prior Art
Engines indispensably need lubricating systems mainly to achieve smooth and efficient operation and also to minimize wear in engine moving parts. The lubricating systems use engine oil as a lubricant. A short supply of engine oil increases the resistance to motion among engine parts in contact with one another, thereby degrading engine efficiency and increasing wear on the engine parts.
It is known to equip the engine with an alarm device which generates an alarm signal when engine oil pressure drops below a constant reference level representing an insufficient supply of engine oil. The engine oil pressure is sensed at some point along an oil line connecting the outlet of an oil pump to engine moving parts. Since the oil pump is generally driven by the engine, the engine oil pressure essentially rises according to engine rotational speed. Accordingly, the constant reference level is chosen so that an alarm signal can always indicate a short supply of engine oil even when the engine is idling, that is, when engine rotational speed is low.
Generally, the higher the engine rotational speed, the greater the required supply of engine oil. In such an alarm device, there is, consequently, a problem that no alarm signal will be generated when the supply of engine oil drops just below the required level in the high engine speed range.